Process for strip cladding by hot rolling of particulate material



July 28, 1964 s, STQRCHHElM 3,142,560

PROCESS FOR STRIP CLADDING BY HOT ROLLING OF PARTICULATE MATERIAL 4 Sheets-Sheet 1 Filed NOV. 17. 1960 INVEN TOR. l Samuel. SW1/61M BY W W Array/Veys July 23, 1964 s. sToRcHHElM 3,142,560

PROCESS FOR ST CLA DDING BY HOT ROLLING OF PA CULATE MATERIAL Filed NOV. 17. 1960 4 Sheets-Sheet 2 By 5am Smc/#HEIM A rra/@Nays July 28, 1964 s. sToRcHHElM 3,142,560

PROCESS FOR STRIP CLADDING BY HOT ROLLING OF' PARTICULATE MATERIAL 4 Sheets-Sheet 3 Filed Nov. 17. 1960 INV EN TOR. SAMueL SroWHe/M July-28, 1964. s.s1'oRcH|-|E|M 3,142,560

v PRocEss RoR STRIP CLADDING- BY HOT- ROLLING oF RARHCULATE MATERIAL Filed Nov. 1'?, 1960 4 Sheets-Sheet 4 2. Y I INVENToR.

AMUeL SrofcH//fm Arme/vars States This invention relates to a method and apparatus for the cladding of a metallic base by the hot rolling of metallic particles thereon.

This application is a continuation-impart of my copending applications Serial No. 704,055, filed December 20, 1957, and Serial No. 37,002, led June 17, 1960, now abandoned.

In the cladding of metal bases, regardless of their shape, many and varied techniques have heretofore been followed including liquid metal dipping, electroplating, electroless plating, metal spraying, extrusion, hot pressing, vacuum plating, cold pressing under extremely high pressures, etc.

Attempts have also been made to effect cladding by means of cladding powders, by extruding the powders, by cold pressing and sintering and by other techniques. Each of these prior powder cladding techniques has one or more of the following drawbacks; namely, excessive cost of operation, lack of consistency in the end products or inferior properties.

Accordingly it is the primary object of this invention to provide a novel method and apparatus for effectively cladding a base metal with another metal which initially is in particulate form preferably exceeding powder size.

Among the significant advantages of the present invention are substantially reduced cost and consistent end products with commercially acceptable cladding properties.

More particularly, an object of the invention is the provision of a method and apparatus wherein the cladding metal can be applied in discrete particulate form directly to the metal strip or core to be clad, and subsequently bonded thereto by hot rolling at a temperature within the recrystallization range of the cladding material.

An additional object of the invention is the provision of a method or process whereby continuously fed strips of metal base material may be continuously clad, in the manner set forth in the preceding paragraph, rapidly and inexpensively.

Still another object of the invention is the provision of a method of cladding which includes a metallurgical bonding phenomenon arising from the diffusion of the atoms of the clad materail into the base metal and vice versa, in such manner that they are interbonded, and in certain cases, are united chemically to form intermetallic bonding compounds.

A still further object of the invention resides in the process of cladding a strip with the application of a uniform impervious coating, with the simultaneous metallurgical bonding of the cladding material to the strip to be clad, whereby the clad product attains full density and improved mechanical, physical and chemical properties.

A more specific object of this invention resides particul-arly in a process for the cladding of aluminum particles to a low carbon steel strip.

Yet another object of the invention is to provide improved apparatus for effectively carrying out the abovedescribed processes and methods in accordance with the invention.

Briefly stated, these objects are attained in a process and by apparatus wherein a surface of a base metal is covered with a cladding metal in particulate form, the covered base being rolled While the particles of cladding metal are heated to a point at least above their recrystallization temperature.

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing wherein:

FIG. 1 shows diagrammatically a system for continuously cladding a base strip in accordance with the invention.

FIG. 2 shows in longitudinal section a preferred embodiment of a sheath technique for cladding a metal plate.

FIG. 3 is a vertical cross-section of an apparatus for continuously cladding a base strip.

FIG. 4 is a modification of the apparatus shown in FIG. 3 whereby the base strip is heated electrically.

FIG. 5 is a vertical cross-section of an apparatus for producing a composite metal in Which the base material as well as the cladding layers thereon are initially in particulate form.

FIG. 6 is a photomicrograph showing in longitudinal section the appearance of a cast-wrough carbon steel plate clad with powder fabricated aluminum in accordance with the invention.

FIG. 7 is a photomicrograph showing in longitudinal section a cast-wrought carbon steel plate clad with powder fabricated stainless steel in accordance with the invention.

Referring now to the diagrammatic illustration of FIG. 1, one form of apparatus for carrying out a process in accordance with the invention is shown including a hopper H for feeding particulate material, as discussed in detail hereinafter, on the top surface of a base metal B, the covered base metal being fed through a furnace F after the thickness of the covering layer has been gauged by a suitable device such as a spreader plate or doctor blade G.

The covered metal base emerging from the furnace F is fed through a suitable rolling mill M of any standard design. For purposes of illustration, base metal B is in the form of a flexible metallic strip taken from a reel R, the strip after cladding being rewound on a reel R1. The base metal is first conditioned to provide an oxidefree surface, this being accomplished by abrading brushes A. Such conditioning may also be effected by emery cloth or if desired the strip can be chemically cleaned or degreased, as in the case of a low carbon steel base, by passing the strip through acetone.

The metal particles P may be fabricated of the same metal as the base metal to provide, say, a finer grain surface structure in order to improve the strength of the surface layer. The metal particles P may also be an alloy of the base metal or a similar metal or alloy to provide a variety of properties, such as improved electrical conductivity, corrosion and oxidation resistance, improved abrasion resistance or an enhanced appearance. Cladding may also be effectedV for the purpose of providing a surface which facilitates soldering or lamination such as when a thin layer of iron is bonded to an aluminum base to permit the soldering of two sections of the finished clad strip together by the iron layers.

The particles of metal that have successfully been cladded to a metal base, such as low carbon steel, have varied in size and shape from particles in the powder range, i.e., 1,000 microns in diameter and less, to particles of substantial size such as chunks of titanium sponge having at least one dimension of a half inch or more. The

invention has further been successfully carried out using nodules, pellets, needles, cubes and shot of metal such as aluminum, lead, aluminum-iron alloy and titanium sponge.

Successful results have also been obtained with cladding metal in powder form using aluminum, lead, zinc, tin, stainless steel, aluminum-iron alloy (14% aluminumbalance iron), nickel and titanium.

From the foregoing it will be apparent that the invention lends itself to use with any particulate cladding metal provided that the temperature and rolling pressure conditions are such as to effect integration of the particles into a coherent clad which is bonded to the base metal.

The invention preferably makes use of particulate cladding metals above powder size, that is, where at least one dimension of a particle is greater than 1,000 microns. The advantages which flow from the use of such particles are the reduced cost of particles as compared to powder, the lesser surface area of particles and hence lower oxide content, thereby facilitating bonding and inducing greater ductility in the finished clad. In addition, the particles when vertically fed onto the base plate have a lesser tendency to agglomerate and this makes possible easier and more uniform feeding actions. Y

The base metal B covered with particles of cladding metal to an empirically determined thickness is conveyed into furnace F where the base and the particles thereon are heated in air or in a reducing or inert atmosphere to a temperature at which the particles when introduced between the rolls in the mill for compaction and reduction are at least above their recrystallation temperature, as set forth in greater detail hereinafter.

In the system shown in FIG. l, the cladding is continuous and is effected on one face only of the base metal. FIG. 2 shows a technique for cladding on both sides of the base B. This is done by first abrading and degreasing a base plate B made, for example, of steel in a length which may be readily handled, the plate then being placed within a sheath S closed at one end. The sheath may be made of low carbon steel or any other material which can resist the pressures generated within the sheath during the rolling thereof above the recrystallization temperature of the cladding metal.

The particulate cladding material P is then poured around the base plate B and the sheath S is vibrated by applying a vibrator thereto so that the base plate is centered within the sheath and locked in place by the vibrated powders. The other end of the sheath is then closed and the entire assembly is heated above the recrystallization temperature of the cladding particles. Immediately thereafter, the closed sheath is rolled in mill M to effect the desired compaction of the cladding metal and the bonding thereof to the base plate. After rolling, the sheath is removed from the compact by mechanical stripping or by chemical dissolution.

As in the case of cladding by direct rolling in the manner shown in FIG. l, the thickness of the clad is controllable by varying the initial particle height as determined by the relative dimensions of the plate and sheath, and the reduction given the sheath during rolling.

Referring now to FIG. 3, this illustrates a preferred embodiment of an apparatus for continuously cladding metallic strips with particulate metal in accordance with the process of the instant invention. Generally indicated at is a strip of base material, which may for example be of low carbon steel. The strip 10 is inserted cold or unheated centrally into a hopper indicated at 11. the hopper there is gradually fed suitable particulate, i.e., granular or powdered material P, such as is described hereinafter.

The particulate material P is heated to above its re-A crystallization temperature and fed in discrete form into the hopper 11 on opposite sides of base strip 10 from a pair of rotating heating furnaces 21 and 21', such as are more fully described in my copending application Serial No. 37,002, filed June 17, 1960, now abandoned, which is a continuation of my application Serial No. 696,728, filed November 15, 1957, now abandoned. Furnaces 21 Intoy and 21 are identical in design, hence only the furnace 21 is particularly described.

The furnace 21 is mounted within chamber 18 for rotation by a suitable transmission T from motor 41. The particulate material P is fed to the furnace 21 through anopening 114 in the top 113 of the chamber 18. The cover plate 116 is removable from opening 114 along guides 115 for introducing the material P through the opening 114.

Directly underlying the opening 114 is a storage hopper 11S, having a downwardly converging bottom wall 119, which empties into a spout 20. The spout 20 is positioned to discharge into the furnace 21. Furnace 21 is mounted for rotation in an inclined position within a bearing structure 24, carried by Van upstanding inclined bracket 25, which is in turn mounted on a support (not shown), carried by the base of the chamber 18. The inclination of the furnace is such as will allow gravity feed of the heated particulate material. The furnace 21 is rotatable within heating coil 128, preferably of the electrical type, and supplied with electrical currentfrom a suitable source through electrical leads 22 which pass through an insulator 23. Heating coil 128 serves to heat the furnace so that the particles of material P within the furnace attain a suitable temperature above the recrystallization temperature of the material P, as discussed in detail hereinafter.

A mounting bracket 29 is provided for supporting the upper end of the furnace 21. Attached to bracket 29 is an apertured portion 30 which is forwardly and upwardly inclined, the latter being provided with an outwardly extending arm 31 which serves as a journal for a shaft 32. The shaft 32 is driven by a belt transmission 38 trained over pulleys 137, 131, the latter being driven by motor 41. A gear 33 on shaft 32 is in mesh with a ring gear 34 carried by the furnace 21, and an outstanding journal member 134 at the opposite end of the bracket portion 30 carries a shaft 35, upon which is mounted an idler gear 36, which also serves as a guide and meshes with ring gear 34.

The rotation of the furnace is concurrent with the heating of the particulate material therein and suciently agitates the material to prevent agglomeration thereof. v The lower ends of the furnaces 21 and 21 are of inverted frusto-conical form, as shown at 43 and 43', and are provided at their lower end with an opening through which the heated particulate material P can flow into the funnel-shaped receiving hopper 11 on opposite sides of the base strip 10 passing therethrough. The shape of the funnel-like hopper 11 and its lower portion 11b is designed to direct the particulate material P passing from the furnace 21 thereto into a relatively thin elongated plane, and to guide it along the surface of the base 10. A vibrator V is attached to hopper 11 to assist in spreading the material P uniformly acrossI the opposing surfaces of the base.

An induction coil 13 surrounding the hopper 11 serves to maintain the particulate metal P, such as aluminum, at its desired temperature above its recrystallization temperature for subsequent hot rolling through pressure rolls 15. i

The strip after passing through the receiving hopper 11 and being coated on both sides with suitable particulate material P passes between the rolls 15 and issues in consolidated or clad form, as shown at 16. By means of appropriate design of the receiving hopper 11, its guide portion 11b, and limited only by the width of the rolls and the hopper, any desired width or shape of strip may be so clad, and the process is substantially continuous.

After the material has passed between the rolls 15, it is coiled as shown at 17 or it may be passed out from the chamber in any other desired manner, such as through an opening having a gasket type seal, as shown in the above-mentioned copending application Serial No. 37,002.

Under certain circumstances, such as when the metal P is easily oxidized at elevated temperatures, it is desirable that the product be protected from atmospheric contact during the course of the operation, in which case the furnace and cladding apparatus is enclosed in a sealed chamber 18 which is air-tight, and which is provided with an inlet 19 and an exit 20, by means of which the chamber may be either evacuated or filled with an inert gas such as argon or a reducing gas such as hydrogen, the choice being dependent on the particular cladding material being used.

For instance, when coating low carbon steel strips with aluminum powder, the presence of air is not detrimental, but in certain other instances the absence of air may be beneficial, as for example when it is desired to chemically unite the metals of a strip or core and a coating particulate material in the absence of oxygen.

The process and apparatus disclosed above provides a base strip or core with a suitable particulate cladding material, the atoms of the cladding material being diffused into the base or core and vice versa, and the atoms in many instances being not only diffused, but so rearranged as to provide chemically united intermetallic compounds, which act as further bonding agents. Such compounds as FeAl3 in a case of cladding steel with aluminum particulate material can also supply additional properties to the bond as, for example, in providing greater corrosion protection.

Various additional steps may also be integrated into the processes above described with respect to FIG. 3. For example, if necessary, the step of cleansing the strip may be incorporated into the process just prior to the entry of the strip into the hot particulate material at 11, and the final clad thickness at 16 may be closely controlled within predetermined dimensions by means such as adjustment of the roll gap, increasing the particle size, varying the thickness of the uncompacted layer, or increasing the temperature.

Referring now to FIG. 4, this illustrates an alternate embodiment of the process of FIG. 3, wherein the base strip 10', instead of being introduced in the hopper in cold condition, is heated electrically from a source E of electricity. The resilient contacts C-1 and C-2 engage the moving surface of the base strip 10 and are electrically connected in parallel through a resistance X to one terminal of the electrical source E. The two pressure rolls are also electrically connected in parallel and are joined to the other terminal of the electrical source E.

Thus, current flows from source E through the resistance path including the base strip 10 to effect heating thereof. The particulate material P is fed into hopper 11 from a furnace such as 21 in FIG. 3 in a manner similar to that illustrated in that figure. The base strip 10' is heated sufficiently from source E to raise its temperature to that of the particulate material P as it left the furnace. If desired, auxiliary heating can be provided by coils 13 for maintaining the desired temperature of the particulate cladding material P.

As the base strip 10' and the particulate material P pass through the pressure rolls 15 at a speed such as to effect bonding at the temperature existing between the rolls, the cladding material P is hot-rolled onto the surface of the base strip 10 and bond therewith in a manner similar to that above described in the description of FIG. 3, and the cladded strip issues as a finished clad strip shown at 16. In practice, rolling speeds of from 21/2 to 50 feet per minute have been utilized for different claddings.

In the embodiment of FIG. 5, instead of a solid base strip, the base material is in the form of pellets or particulate material 10". As in the embodiment of FIG. 3, the cladding material P" is fed from rotary furnaces 21" into hopper 11 onto each side of the guiding form 50 into which the particulate base material 10 has been fed from a rotary furnace 21". As the base material 10 issues out of the lower end 51 of the guiding form 50, it becomes sandwiched in between the particulate cladding material P in the guide duct 11b. Form 50 depends from an inner hopper and is supported by spider arms Sa within hopper 11". The base particulate material 10" is maintained at a temperature above its recrystallization temperature but below its melting temperature by means of coils or electrical heating elements 52 around the guiding form 50. Likewise, the cladding material P" is maintained at a temperature between its recrystallization temperature and its melting temperature by means of the heating element 13". Consequently, a composite body consisting of an inner layer of base material 10 and two outer layers of cladding material P is formed immediately in advance of rolls 15 and passes through the pressure rolls 15 to hot roll the body into a finished clad product as shown at 16". It is to be understood that the composite body may be composed of two or more layers. i

The process above described not only makes possible the production of superior properties in the resulting clad metals, as well as a metallurgical bonding of the core to the cladding, but also, when desirable, makes it possible to eliminate the need for intermediate alloys in the bond zones. The technique above described is furthermore, inherently, a less expensive fabrication technique than those in present use and is characterized by extreme simplicity as well as reliability.

By a process in accordance with the invention, lead has been bonded to a low carbon steel base of 3A@ of an inch thickness by placing a 1A inch layer of lead particles (Glidden Mfg. Co.-lead particles 40B grade) on the plate, the particles and plate being heated simultaneously to 300 C. The heated combination was then rolled in a 6 x 8 horizontal rolling mill at a speed of about 50 feet per minute with an initial zero clearance between the rolls, the spring back effect of the rolls allowing passage of the combination therethrough. Heating and rolling were both carried out in air.

The thickness of the clad is a function of the initial particle height used as the severity of the reduction and may vary from a few thousandths of an inch or upwards to 1/32 or 3%;4 of an inch. The thickness of the clad may be reduced by further rolling subsequent to the initial consolidation step.

Aluminum has been bonded to a steel base in much the same way as with lead, as above described, except that the steel and aluminum clad particles (Alcoa-Grade particles) were preheated to 600 C. Again heating and rolling were carried out in air. In both the lead and aluminum clad examples given above, the base plate was lirst abraded and degreased. The reduction ratio effected by rolling is important, and the particle reduction ratio in the process according to the invention should be in the neighborhood of 4:1 to 8:1 to obtain a commercially satisfactory product.

In the apparatus shown in FIGS. l, 3, 4 and 5, continuous cladding of strip is effected as contrasted to the more expensive semi-continuous operations characteristic of the sheath rolling technique disclosed in connection with FIG.

2. However, sheath rolling does have the advantage ofV requiring less costly equipment and does not require that a protective atmosphere be used. The sheath S in FIG. 2 completely envelopes the particles and protects them from oxidation, save for the small amount which occurs due to the presence of void spaces between the particles.

Even such small amounts of oxidation can be eliminated by purging the ensheathed particles with hydrogen or inert gas before the open end is closed. If necessary, the sheath can also be evacuated prior to the sealing of the sheath to provide even greater protection for the contents therein.

In the case of the cladding of steel, the characteristics of the powders or particles do not appear to be critical as long as they are reasonably free of oxides or other impurities which might tend to embrittle the clad. However, even materials which are susceptible to oxidation can be clad onto steel by direct rolling in air. For example, in'the cladding of low carbon steel with nickel or stainless steel, the base plate is first abraded and degreased in the usual fashion. About 1A inch of the powder or particles is heaped on the steel plate to be clad, and the resultant combination is then heated in an open-ended hydrogen filled retort until it attains a temperature of 1300 C. The combination is removed from the retort and immediately rolled in air in a 6" X 8 horizontal rolling mill operating at a speed of about 50 feet per minute with a zero initial clearance between the rolls.

In certain situations the rolling mill available may not be sufficiently powered to carry out consolidation of particles heated above their recrystallization temperature but below their melting temperature. In this case, with respect to aluminum particles, I have heated the particles to 700 C. Although this temperature is sufficient to melt aluminum, the normal presence of oxide fihn about each particle prevented the fusion thereof and acted as a protective jacket. When the particles so heated entered the underpowered rolling mill, they became sufficiently cooled by contact therewith to fall below their melting temperature, whereby the particles were consolidated in the manner described above, the rolling serving also to break the oxide film to permit the particles to bond together and to the base. Similar results were obtained with lead particles heated to their melting point.

The cladding technique disclosed herein is not limitedV to the clad materials discussed hereinabove but is adaptable to a wide variety of materials. The following table illustrates the wide variety of material which can be clad on carbon steel strip and the fabrication conditions necessary for such operation. The figures below are with respect to a powder height of 1A inch, a steel base of VLG inch and a rolling speed of 44 feet per minute. In connection with the following table, all materials were clad using particles in the powder range, but in the cases of aluminum lead, titanium and aluminum-iron alloy (14% Al-balance Fe), large particles above powder size were also clad under the same speed, temperature and atmosphere conditions. In fact, chunks of titanium of 1/2 inch minimum size were clad and nodules and cubes of ls to 1%; inch size of aluminum, lead and aluminumiron alloy were successfully clad under the conditions indicated in the table and at the same rolling speed mentioned above.

Fabrication Conditions Necessary for Cladding Various Malerials on Carbon Steel In cases of metals clad in accordance with the invention, I have found that the clad may be bent 180 without having the clad crack or break away from the base metal. In some instances, the clad emerges from the rolling mill in a slightly cold worked condition so that annealing is necessary in order to develop a clad which is fully resistant to eXure and which will not crack or peel away from the base metal. Cold working is due to the quenching action of the cold rolls and can be greatly reduced by keeping the rolls hot. This can be accomplished by means of gas burners using direct flame impingement on the rolls or by electric cartridge heaters located within the rolls.

In FIGS. 6 and 7, samples of cladded plate fabricated by hot rolling are sectioned for metallographic examination. The photomicrograph in FIG. 6 shows an unetched section of a carbon steel plate clad with powder rolled aluminum product. Oxide inclusions will be seen in the clad and a narrow diffusion bond is apparent between the clad and base metal. The irregularity of the juncture between clad and base is due to deformation of the base metal occurring during rolling.

In FIG. 7, there is shown a nickel powder productcarbonsteel cast wrought product bond characterized by the absence of a distinct diffusion zone. The cleanliness of the powder rolled structure shown herein is attributed to the'use of a hydrogen reduced powder feed.

From the foregoing, it will be seen that there is herein set forth an improved method and apparatus for cladding metal bases by hot rolling of particulate materials onto the base, which accomplishes all of the objects of this invention, as well as providing many advantages of great practical utility and commercial importance.

It will be obvious to those skilled in the art, upon a study of this disclosure, that the present invention permits of various modifications and alterations with respect to the individual components of the apparatus and the method steps herein disclosed, and hence can be embodied in equipment and processes other than particularly illustrated and described herein, without departing from the essential features of the invention and within the scope of the claims annexed hereto.

I claim:

1. The process of cladding at least one surface of a metal base with a cladding metal comprising heating a mass of cladding metal in particulate form to raise the temperature of the particles to a point above the recrystallization temperature thereof but below a temperature at which melting of the outer surfaces of said particles occurs, passing a metal base to and through said mass while confining a layer of heated particles against said surface to cover the same, while maintaining said particles in discrete form, and hot-rolling said covered base while said particles are heated above their recrystallization temperature at a speed sufficient to bond the particles of the layer to one another for the first time and to clad said base.

2. The process of claim 1 and applying heat directly to said base while it is passing through said mass.

3. The process of claim 1 in which said particles are agitated to maintain them in discrete form prior to rolling.

4. The process of claim 3 in which said base is passed vertically through said mass directly into the nip of a set of work rolls.

5. The process of metal cladding a ferrous metal base comprising feeding cladding metal in particulate form to and through a heating zone, applying heat in said zone to such particles to raise the temperature thereof above the recrystallization temperature of the metal while agitating the particles to prevent agglomeration thereof, continuing the feed of the now heated particles by gravity into and through a confining zone having a lower constricted portion of adjustably fixed dimensions, concurrently with the passage of particles through said confining zone continuously feeding a metal base through said confining zone in contact with said particles whereby in the concurrent passage of base and particles through said lower constricted portion a uniform layer of heated particles covers at least one surface of said metal base, the thickness of said layer being determined by the thickness of the metal base and the dimensions of the lower constricted portion of the confining zone immediately after said base and layer issue from said lower portion of the confining zone, passing the same through metal rolls to bond the particles of the layer to one another and to clad the adjacent surfaces of the base with -the metal of the particles and effecting such rolling while the temperature of all the particles is above their recrystallization temperature.

n' 6. The process as claimed in claim and applying heat directly to said metal base while it is passing through said confining zone.

7. The process as claimed in claim 6 in which said base is passed centrally through said confining zone so that uniform layers of heated particles are applied against opposite surfaces of the base.

8. The process of metal cladding a ferrous metal base comprising feeding cladding metal in particulate form of a nodular character having a size of at least l mm. in at least one direction to and through a heating zone, applying heat to such particles in said zone to raise the temperature thereof above the recrystallization temperature of the metal while agitating the particles to prevent agglomeration thereof, continuing the feed of the now heated particles by gravity into and through a confining Zone having a lower constricted portion of adjustably fixed dimensions, concurrently with the passage of particles through said confining zone continuously feeding a metal base through said confining zone in contact with said particles whereby in the concurrent passage of base and particles through said lower constricted portion a uniform layer of heated particles covers at least one surface of said metal base, the thickness of said layer being determined by the thickness of the metal base and the dimensions of the lower constricted portion of the confining zone immediately after said base and layer issue from said lower portion of the confining zone, passing the same through metal rolls at a rate of from 21/2 to 50 feet per minute to bond the particles of the layer to one another and to clad the adjacent surface of the base with the metal of the particles, and effecting such rolling While the temperature of all the particles is above their recrystallization temperature.

9. The process of metal cladding a metal base comprising applying heat to particulate cladding metal to raise the temperature thereof above the recrystallization temperature but below the temperature at which the surfaces of the metal particles melt,

feeding the heated particulate cladding metal by gravity into and through a conning zone having a lower constricted portion of fixed dimensions,

concurrently with the passage of particles through said confining zone continuously feeding a metal base through said confining zone in contact with said particles, while maintaining the particles in discrete form, so that, in the concurrent passage of base and particles through said lower constricted portion, a uniform layer of heated particles covers at least one surface of said metal base, the thickness of said layer being determined by the thickness of the metal base and the dimensions of the lower constricted portion of the confining zone immediately after said base and layer issue from said lower portion of the confining zone,

passing the same through metal rolls to bond the particles of the layer to one another and to clad the adjacent surface of the base with the metal of the particles,

and effecting such rolling while the temperature of all the particles is above their recrystallization temperature and below said melting temperature.

10. The process as claimed in claim 9 in which said base is passed centrally through said confining zone so that uniform layers of heated particles are applied against opposite surfaces of the base.

11. The process of claim 9 in which the particles are maintained in discrete form by vibration thereof.

12. Apparatus for cladding a metal base with metal cladding material comprising receiving means for a supply of particulate metal cladding material, a hopper, means for heating said particulate material above its recrystallization temperature and for transferring such particulate material between said receiving means and said hopper, means for vibrating said hopper to prevent agglomeration of heated particles therewithin, a shaping duct beneath and in free communication with said hopper, a rolling mill immediately subjacent said shaping duct, and means for feeding a strip of metal base material serially through said hopper, shaping duct and roll whereby in such passage a layer of particulate cladding material covers at least one surface of said strip within said feeding duct, and the strip and layer are bonded in said rolling mill to produce a cladded metal base.

13. Apparatus as claimed in claim 12 and further including means for heating said hopper so as to maintain the temperature of the particulate material within the hopper and duct above its recrystallization temperature.

14. Apparatus as claimed in claim 12 and further including means for directly heating said strip.

15. Apparatus as claimed in claim 12 in which the means for feeding the strip positions the same centrally of said feeding duct so that during passage therethrough uniform layers of particulate cladding material are applied against opposite surfaces of said strip so that the resultant hot-rolled strip and layers is a composite structure of base and cladding on opposite surfaces of the base.

16. Apparatus for cladding one metallic material with another comprising a hopper, a shaping duct extending beneath said hopper and in communication therewith, a second hopper, a second feeding duct communicating with said second hopper and disposed centrally within said first feeding duct, said second feeding duct having a shape complemental to the shape of the first feeding duct but having reduced dimensions such that a space is provided between opposite external surfaces of the second duct and the facing internal surfaces of the rst duct, said second duct having a terminal end adjacent the terminal end of the first duct, means for heating and feeding particulate metallic material into each hopper, means for vibrating said hopper whereby such particulate metallic material feeds by gravity through the second duct and the spaces between the ducts, said heating and feeding means being effective to raise the temperature of the particulate metallic materials above their recrystallization temperatures, and a rolling mill having rolls disposed immediately subjacent 4the terminal ends of said ducts whereby heated particulate material of composite form, including an intermediate layer of one metallic material and opposite external layers of another metallic material are heated to a temperature above their recrystallization temperatures and are hot-rolled to form a composite metallic body.

References Cited in the file of this patent UNITED STATES PATENTS 2,289,658 Koehring July 14, 1942 2,320,801 Simons .lune 1, 1943 2,341,732 Marvin Feb. 15, 1944 2,352,443 Mautsch June 27, 1944 2,815,567 Gould et al Dec. 10, 1957 OTHER REFERENCES Wulff: Powder Metallurgy, The American Society for Metals, Cleveland, Ohio, 1942, pp. 51-53. 

1. THE PROCESS OF CLADDING AT LEST ONESURFACE OF A METAL BASE WITH A CLADDING METAL COMPRISING HEATING A MASS OF CLADDING METAL IN PARTICULATE FORM TO RAISE THE TEMPERATURE OF THE PARTICLES TO APOINT ABOVE THE RECRYSTALLIZATION TEMPERATURE THEREOF BUT BELOW A TEMPERATURE AT WHICH MELTING OF THE OUTER SURFACES OF SAID PARTICLES OCCURS, PASSING A METAL BASE TO AND THROUGH SAID MASS WHILE CONFINING A LAYER OF HEATED PARTICLES AGAINST SAID SURFACE TO COVER THE SAME, WHILE MAINTAINING SAID PARTICLES IN DISCRETE FORM, AND HOT-ROLLING SAID COVERED BASE WHILE SAID PARTICLES ARE HEATED ABOVE THEIR RECRYSTALLIZATION TEMPERATURE AT A SPEED SUFFICIENT TO BOND THE PARTICLES OF THE LAYER TO ONE ANOTHER FOR THE FIRST TIME AND TO CLAD SAID BASE.
 12. APPARATUS FOR CLADDING A METAL BASE WITH METAL CLADDING MATERIAL COMPRISING RECEIVING MEANS FOR A SUPPLY OF PARTICULATE METAL CLADDING MATERIAL, A HOPPER MEANS FOR HEATING SAID PARTICULATE MATERIAL ABOVE ITS RECRYSTALLIZATION TEMPERTURE AND FOR TRANSFERRING SUCH PARTICULATE MATERIAL BETWEEN SAID RECEIVING MEANS AND SAID HOPPER, MEANS FOR VIBRATING SAID HOPPER TO PREVENT AGGLOMERATION OF HEATED PARTICLES THEREWITHIN, A SHAPING DUCT BENEATH AND IN FREE COMMUNICATION WITH SAID HOPPER, A ROLLING MILL IMMEDIATELY SUBJACENT SAID SHAPING DUCT, AND MEANS FOR FEEDING A STRIP OF METAL BASE MATERIAL SERIALLY THROUGH SAID HOPPER, SHAPING DUCT AND ROLL WHEREBY IN SUCH PASSAGE A LAYER OF PARTICULATE CLADDING MATERIAL COVERS AT LEAST ONE SURFACE OF SAID STRIP WITHIN SAID FEEDING DUCT, AND THE STRIP AND LAYER ARE BONDED IN SAID ROLLING MILL TO PRODUCE A CLADDED METAL BASE. 